Eating too much sugar on antibiotics could squash helpful gut bacteria

While a spoonful of sugar might help us gulp down a bitter-tasting antibiotic, it also may increase the damage that these drugs cause to the gut microbes.

In patients being treated for blood cancers, eating sugary items during antibiotic treatment was linked to a greater reduction in gut bacteria diversity than taking the antibiotics alone. The combination was also tied to the growth of gut bacteria associated with hard-to-treat infections, researchers report September 30 in Nature.

Cancer patients have lots of variation in their diets and take medications that can damage their microbiome. So, these patients provide a unique opportunity to study dramatic gut changes “that we believe are also relevant in the healthy context,” says Jonas Schluter, a microbiologist at NYU Langone Health.

Previous evidence separately suggested that antibiotics and sugars can disrupt the gut microbiome. But their combined effects, particularly in people at greater risk of infection, was unclear.

Researchers closely tracked more than 9,000 meals eaten by 173 people hospitalized in a treatment center to undergo blood-forming stem cell transplants. “Diet records are one of the biggest black boxes in a lot of diet microbiome studies,” since meals are often self-reported, says Tiffany Weir, a microbiologist at Colorado State University in Fort Collins, who was not involved in the research.

Standardized hospital meals allowed researchers to measure multiple days’ worth of food intake down to the gram, then compare the amounts of various nutrients eaten with bacterial diversity data obtained from stool samples.

For every additional 100 grams of sugar (the equivalent of 2.5 cans of Coke) that patients on antibiotics ate in the two days before sampling, the team found a 24 percent decrease in bacterial diversity. Consuming sweets and sugary beverages during antibiotic treatment was also associated with blooms of Enterococcus bacteria, which can be drug-resistant and are linked to difficult-to-treat infections associated with longer hospital stays and higher mortality.

“Some bacteria, sometimes, survive antibiotics, or perhaps more dangerously, they are resistant to [them],” Schluter says. By giving these bacteria the “universal resource for life, which is simple sugars, we are exacerbating their dominance. It’s almost like burning down the rainforest with a lot of fire, and then trying to extinguish the flames by putting in more petrol.”

The researchers also exposed mice on standard or sucrose-rich diets to a single dose of antibiotics. They found that the sugar exacerbated the enterococcal abundance after antibiotic exposure. 

“Reducing sugar intake could be another way for patients to support their gut microbiome during antibiotic treatment,” says Sarah Berry, a nutrition scientist at King’s College London who was not involved in the study. Still, more research is needed to determine whether the findings apply to anyone on these drugs.

Schluter hopes that further studies and clinical trials can help uncover more about the exact relationship between sugar, antibiotics and the gut microbiome.

“You need to take antibiotics to fight infections, but you should also be aware that they have side effects to the microbiome,” Schluter says. “Now, we need to find strategies to mitigate this damage.”